XXXIII.—The Blood Vascular System of the Spiny Dogfish, Squalus acanthias Linné, and Squalus sucklii Gill

The following investigation was commenced, in the first place, to provide information for class use, for, in spite of the fact that thousands of specimens of Squalus acanthias and S. sucklii are used every year in North America, there appears to be no satisfactory account of the blood vascular system of either species available. As the work proceeded, various problems arose which necessitated references to the conditions in other species and the preparation of more detailed dissections than are usually made in class work. It is well known that there is considerable confusion in the nomenclature employed by different authors for even some of the main vessels, and it was soon evident that this is not merely individual preference but, in part, due to a more fundamental lack of agreement as to the precise morphological significance of the vessels themselves. More recent embryological investigations by other workers have, we consider, given a key to the solution of the most important of these problems and have shown that, in so far as the blood-vessels are concerned, the Elasmobranchs lie closer to the other gnathostomatous vertebrates than is generally recognised, and indeed furnish a primitive and generalised type. The time seemed ripe, therefore, to provide a connected account of the vascular system in an Elasmobranch, viewing it in the light of the researches just referred to, and of what is known of the distribution of the various vessels in the sub-class in general. It was hoped that this would provide an epitome that would serve as a basis for future work in the sub-class, and also for comparison with the conditions in higher vertebrates.